1. Field of the Invention
The present invention relates to a metal gasket assembly comprised primarily of metal components such as stainless steel plates.
2. Description of the Related Art
A conventional metal gasket assembly generally comprises one or more metal plates having openings and beads formed around the openings. Such a metal gasket assembly is typically used in an internal combustion engine as a seal between a cylinder block and a cylinder head.
To improve the sealing effect of a metal gasket assembly, there has been proposed to attach a shim to a substrate metal sheet at a region surrounding a cylinder opening so that the fastening pressure applied to the metal gasket assembly is locally increased in that region.
However, the conventional metal gasket assembly interposed between the cylinder block and the cylinder head requires a strong fastening by bolts for effective sealing, and thus it may cause a deformation in the cylinder head. Particularly, in a portion around a combustion chamber, the deformation in the cylinder head tends to increase the size of a gap formed between the cylinder block and the cylinder head. This gap allows an escape of combustion gases from the chamber, which leads to a contamination of the metal gasket assembly and hence, to a gradual deterioration of the seal between the cylinder block and the cylinder head.
Moreover, since the size of the gap around the combustion chamber changes corresponding to the change of combustion pressure in the internal combustion engine, beads provided on the metal gasket assembly is subjected to an alternate load of compression and restoration, thereby giving rise to fatigue of the beads on the metal gasket assembly. The fatigued beads with reduced elasticity weaken the fastening function of bolts, with the result that the sealing effect of the metal gasket assembly is decreased.
Furthermore, in the case of a metal gasket assembly employing a shim ring, the thickness of the shim ring is significantly influential on the sealing performance of the metal gasket assembly. However, it is difficult to adjust the shim thickness to 0.05 mm or less, because of difficulties in producing, with a sufficient accuracy, a plate of such thickness for the use as a shim.